Several media outlets have indicated law enforcement is focusing on a Saudi Arabian national, but POLITICO did not immediately confirm the nationality of the foreigner drawing attention from the authorities.

At a Monday evening press conference, Boston Police Commissioner Ed Davis said there was no “suspect” at Brigham and Women’s Hospital, as other reports indicated, but he acknowledged that “there are people we’re talking to.”

President Barack Obama on Monday vowed that whoever carried out the bombings near the world-famous race’s finish line would be found and brought to justice.

“We still do not know who did this or why, and people shouldn’t jump to conclusions before we have all the facts,” Obama said in a televised briefing from the White House. “But, make no mistake, we will get to the bottom of this, and we will find out who did this, we’ll find out why they did this. Any responsible individuals, any responsible groups, will feel the full weight of justice.”

Obama addressed the nation Monday evening after law enforcement officials tightened security at the White House and in Washington, New York City and elsewhere following the two explosions that rocked Boston near the finish line of the city’s world-famous marathon, killing at least three people, the Boston police commissioner told reporters at a press conference Monday night. An 8-year-old boy was among the dead, reports said. The blasts injured at least 144 — some critically — and sparked fears of terrorism.

Obama was briefed on the incident — which he did not call a terrorist attack — earlier in the day. While Obama didn’t use the word terrorism in his address to the county, the White House did.

“Any event with multiple explosive devices — as this appears to be — is clearly an act of terror, and will be approached as an act of terror,” a White House official said. “However, we don’t yet know who carried out this attack, and a thorough investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic.”

The president, who learned about the explosions around 3 p.m., called Boston Mayor Tom Menino and Massachusetts Gov. Deval Patrick and received briefings from officials, including Homeland Security adviser Lisa Monaco and other members of his senior White House staff, a White House official said. The FBI looks to take the lead on the investigation, officials said at the Monday night presser in Boston. Officials called it an ongoing criminal investigation that could, potentially, turn into a terrorism investigation.

The president was also briefed by FBI Director Robert Mueller and Homeland Security Secretary Janet Napolitano. The briefings covered the “active investigation and response to the incident in Boston, including the ongoing coordination with state and local officials, a White House official said.

“I’ve updated leaders of Congress in both parties, and we reaffirmed that on days like this there are no Republicans or Democrats — we are Americans, united in concern for our fellow citizens,” Obama said in his public remarks.

Sen. Dianne Feinstein, chair of the Senate Intelligence Committee, said she has been in touch with U.S. intelligence agencies and none had any warning of the bombings.

Feinstein (D-Calif.) called the bombing a “terrorist incident” but said it remained unclear whether it was domestic or foreign.

“Right now I don’t think there are any hallmarks other than the fact that it could be either, it could be homegrown or foreign,” she said, also noting, “My understanding is that it’s a terrorist incident, that it’s an incident with a bomb.”

Sens. Susan Collins (R-Maine) and Angus King (I-Maine) said in a statement that the attacks bear “the hallmarks of a terrorist attack.”

Rep. Michael McCaul (R-Texas), the chairman of the House Homeland Security Committee, told reporters that the Boston explosions “have all the hallmarks of an active terrorism” incident.

Rep. Peter King (R-N.Y.), the former chairman of that committee who is still a member, told POLITICO that “the definite feeling right now is that it’s Al Qaeda or an Al Qaeda affiliated group. But again it could be somebody else but that’s the feeling right now.”

King added that Al Qaeda in the past has called for attacks at athletic events.

“All the signs are there: two attacks, sophisticated weapons, they were able to breach security, it was very sophisticated,” King said.

The FBI is expected to brief the House Intelligence Committee on Tuesday.

“The Boston marathon is about celebration,” Sen. Elizabeth Warren (D-Mass.) told POLITICO in Boston, near tears. “But like the marathoners, the people of Boston are tough and resilient. We will survive this.”

In Washington, the White House upped security outside the building with the Secret Service establishing a broader “secure perimeter” that moved people away from the area.

“Metro is taking this step in an abundance of caution,” said the transit agency in a release. “There is no specific or credible threat against the Metro system at this time.”

Meanwhile, Speaker John Boehner (R-Ohio) led the House in a moment of silence when the chamber gathered for its first votes of the week and called for flags at the Capitol to be lowered to half staff. He also spoke with Obama about the incident, an aide said.

“Words cannot begin to express our sorrow for the families who are grieving so suddenly right now,” Boehner said. “The House of Representatives offers its prayers to the victims and the city of Boston. We also give thanks for the professionals and Good Samaritans who prevented further loss of life.”

Elsewhere on the Hill, U.S. Capitol Police were keeping an eye on developments out of Boston.

“The USCP is monitoring the situation in Boston and is in constant contact with our local and national law enforcement partners as it pertains to the events,” a statement read.

A representative for the Justice Department said officials from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene.

“Attorney General Holder has directed the full resources of the Justice Department to be deployed to ensure this matter is fully investigated,” the DOJ representative also said. “The U.S. Attorney’s Office for the District of Massachusetts is coordinating the Justice Department response with FBI, ATF and other federal, state and local law enforcement authorities.”

New York law enforcement also bolstered security.

“As law enforcement authorities investigate today’s explosions in Boston, I ask all New Yorkers to keep the victims and their families in your thoughts and prayers,” New York City Mayor Michael Bloomberg said, noting security was boosted at key locations “including our subways.”

“We have 1,000 members of the NYPD assigned to counterterrorism duties, and they — along with the entire NYPD and the investments we have made in counterterrorism infrastructure — are being fully mobilized to protect our city,” Bloomberg said in a the statement.

“I have directed state agencies, including the Division of Homeland Security and Emergency Services, State Police, the MTA and the Port Authority, to be on a heightened state of alert as we learn more about this incident,” New York Gov. Andrew Cuomo said.

The security measures taken in Washington and New York and some other cities across the country appeared to be of a precautionary nature, not the result of direct threats. Across the country, security at Los Angeles International Airport and at Dodgers games was also beefed up.

The marathon drew nearly 27,000 participants, NBC News noted, while other reports said the annual event often draws as many as 500,000 spectators. The race unfolded on Patriots’ Day, a Massachusetts state holiday.

Citing an intelligence official, The Associated Press reported that two additional explosive devices were found in Boston and were being dismantled. Later Monday, The New York Times reported that three additional devices were found. Another report from The Wall Street Journal said that five additional “suspect devices” were found, citing counterterrorism officials. The devices were thought to potentially be undetonated explosives, but a later report from the Journal said they were no longer expected to be bombs.

Some reports also said the explosions could have been triggered by remote detonation.

“This is a horrific day in Boston,” Patrick (D-Mass.) said. “My thoughts and prayers are with those who have been injured. I have been in touch with the president, Mayor Menino and our public safety leaders.”

The Federal Aviation Administration had limited airspace around the sites of the explosions in the aftermath. Flights into Boston’s Logan airport were temporarily halted but were back to normal later in the afternoon.

Business did not look to continue as usual on Capitol Hill Tuesday: Senate aides said the press conference scheduled for Tuesday morning to announce an immigration deal would be canceled out of respect for the victims in Boston.

Lawmakers and other officials were quick to weigh in, offering thoughts and prayers.

“Our prayers are with those people in Boston who have suffered injuries,” Vice President Joe Biden said during a call he was on with gun control advocates. “I don’t know how many there are.”

”As I’m speaking, they just turned on the television in my office and apparently there has been a bombing… I don’t have any information,” Biden said.

“Our hearts are heavy with the news out of Boston today. #PrayforBoston,” tweeted Mitt Romney, the former Massachusetts governor and 2012 GOP nominee. His son, Tagg, tweeted cheerfully about the marathon earlier in the day before adding later that he and his family avoided the explosion.

“We r OK. Left Fenway in a cab a few mins before the explosion. Thanks for everyone’s concern. Our prayers are w the victims,” he tweeted.

“My thoughts and prayers go out to the runners, their families, and the City of Boston,” tweeted former Sen. Scott Brown (R-Mass.).

Rep. Ed Markey (D-Mass.), another Senate hopeful, also suspended his campaign activities in light of the events in Boston.

“In response to reported explosions at the site of the Boston Marathon, the Ed Markey for Senate has suspended campaign activities including canvassing, phone banking, fundraising and television advertisements,” a statement from the campaign read.

“Federal, state, and local law enforcement agencies continue to respond and at the President’s direction, the Department of Homeland Security is providing any support necessary in this ongoing investigation,” Homeland Security Secretary Janet Napolitano said in a statement. “We encourage the public to be vigilant, and to listen to direction from state and local officials.”

Earlier Monday, reports highlighted an explosion from the JFK Library, but that blast later appeared to be tied to an unrelated fire.